Tuyển tập các báo cáo nghiên cứu về hóa học được đăng trên tạp chí hóa hoc quốc tế đề tài : Identifying time-varying channels with aid of pilots for MIMO-OFDM | Tang and Leus EURASIP Journal on Advances in Signal Processing 2011 2011 74 http content 2011 1 74 o EURASIP Journal on Advances in Signal Processing a SpringerOpen Journal RESEARCH Open Access Identifying time-varying channels with aid of pilots for MIMO-OFDM Zijian Tang1 2 and Geert Leus2 Abstract In this paper we consider pilot-aided channel estimation for orthogonal frequency division multiplexing OFDM systems with a multiple-input multiple-output setup. The channel is time varying due to Doppler effects and can be approximated by an oversampled complex exponential basis expansion model. We use a best linear unbiased estimator BLUE to estimate the channel with the aid of frequency-multiplexed pilots. The applicability of the BLUE which is referred to as the channel identifiability in this paper relies upon a proper pilot structure. Depending on whether the channel is estimated within a single OFDM symbol or multiple OFDM symbols we propose simple pilot structures that guarantee channel identifiability. Further it is shown that by employing more receive antennas the BLUE can combat more effectively the Doppler-induced interference and therefore improve the channel estimation performance. Keywords MIMO OFDM BLUE time-varying channel pilot-aided channel estimation BEM 1 Introduction Orthogonal frequency division multiplexing OFDM systems have attracted enormous attention recently and have been adopted in numerous existing communication systems. OFDM gains most of its popularity thanks to its ability to transmit signals on separate subcarriers without mutual interference. To further enhance the capacity of the transmission link OFDM systems can be combined with multiple-input multiple-output MIMO features. The fact that OFDM can transmit signals on separate subcarriers can be mathematically represented in the frequency domain by a diagonal channel matrix. This property holds only in a situation where the channel stays almost constant for at
